Abstract:To effectively control the discharge noise of urban landscape dams, the RNG k-ε turbulence model and FW-H acoustic model were used to simulate the flow field and noise of dam discharge. The influence of different hydraulic parameters on the discharge noise characteristics was analyzed. The results show that with the increase of flow rate or water depth over the weir, the discharge velocity and dynamic pressure increase, the degrees of water turbulence and vortex in the stilling pool intensify, and the sound pressure level and sound power spectral density of noise increase. With the increase of downstream water depth, the discharge velocity and dynamic pressure decrease, and the sound pressure level and sound power spectral density of noise decrease. The dominant frequency of discharge noise ranges from 500 to 1 000 Hz under different flow rates and downstream water depths, and it ranges from 500 to 1 200 Hz under different water depths over the weir. The discharge velocity is significantly positively correlated with the sound pressure level in the discharge area and the sound power spectral density in the non-overflow side wall area. The turbulent kinetic energy is significantly positively correlated with the sound pressure level in the discharge area and the sound power spectral density in the discharge section. The dynamic pressure is significantly positively correlated with the sound pressure level in each region and the sound power spectral density in the discharge area. There is a significant positive correlation between the vorticity and sound pressure level in the side wall area of non-overflow section. There is no significant correlation between the flow field factors and the main frequency of the discharge noise.

Abstract:Based on the method of characteristics for hydraulic transient analysis in pressurized water conveyance systems, both simplified and refined mathematical models were derived to characterize the hydraulic behavior of a corridor-shaped water-diversion surge chamber with bifurcation layout upstream. Corresponding computational models for the hydraulic transition process of the water conveyance and hydropower systems were established, with a focus on investigating the surge wave characteristics, local flow regime, and their impacts on regulation guarantee calculations under asymmetric operation conditions. The computational results show that compared with the simplified model, the refined model can accurately describe the hydraulic characteristics of the corridor-shaped surge chamber. While obtaining the extreme values of surge waves and parameters for regulation guarantee calculations, the refined model precisely captures the attenuation characteristics of water level fluctuations in the surge chamber under asymmetric operation conditions. Under asymmetric operation conditions of the units, significant longitudinal flows occur within the corridor-shaped surge chamber, which may affect the hydraulic oscillation characteristics and stability of the system under certain conditions.

Abstract:In order to understand the mechanism of bubble curtains in shallow water, clarify their hydrodynamic characteristic parameters, and investigate the influence of water depth and air supply rate per unit width on these parameters, a numerical simulation study on the hydrodynamic characteristics of bubble curtains was conducted using OpenFOAM based on the two-fluid model. Methods were proposed for the estimation of vertical velocity, horizontal flow velocity, and maximum efficiency of bubble curtains in shallow water. The results show that in the range from a water depth of 0.5 m to 0.2 times the water depth, the central velocity of the bubble plume remains constant along its path, and the horizontal width of the bubble plume increases linearly. At a distance of 0.25 times the water depth from the bubble curtain, the surface flow velocity reaches its maximum, and the thickness of the horizontal flow is the minimum. Then, the surface flow velocity decreases linearly along the flow path. The horizontal thickness ranges from 0.15 to 0.4 times the water depth.

Abstract:To address the complicated groundwater seepage conditions in water-rich sand layer under riverbed influenced by sea tide, the single-borehole dilution method was employed to measure both vertical and horizontal groundwater flow velocities within boreholes, so as to determine the groundwater movement patterns under the fluctuation of river stage. Field test results indicate that the fluctuation of river stage has little impact on the groundwater seepage on both banks, but has great impact on that of alluvial sand bar. If the river stage decreases, the water level of alluvial sand bar will be higher than the river water level, resulting in downward vertical flow in the boreholes. Conversely, when the river stage rises, the water level of alluvial sand bar will be lower, leading to upward vertical flow in the boreholes. The upper silty sand layer of the formation has a certain degree of impermeability, weakening the influence of river water on the deeper strata. As a result, there is no obvious vertical flow in the underlying sand and pebble layer, in which the maximum horizontal flow velocity is as low as 0.48 m/d and will be in favor of the implement of the freezing method.

Abstract:To address the issues of low efficiency and insufficient accuracy in manual calibration of runoff and peak time for multi-parameter urban hydrological models, this study proposed an automatic parameter calibration method based on the improved particle swarm optimization (PSO) algorithm. The method introduces Logistic mapping for particle initialization and Lévy flight for position updating within the PSO framework to avoid local optima. Additionally, considering the characteristics of urban runoff generation and concentration processes, a weighted multi-objective fitness function incorporating overall fitting, peak flow, and peak time was constructed to enhance the model’s ability to capture key hydrological features. The proposed method was implemented in Python and coupled with a mechanistic model (storm water management model, SWMM). Using field monitoring data from a test site, ten key hydrological parameters were calibrated, and the performance of fitness functions with different weight assignments was compared. The results demonstrate that the weighted multi-objective fitness function is more advantageous for urban drainage system emergency management, particularly in improving the simulation accuracy of peak flow and peak time. When applied to a real drainage system in Jiujiang City, the method achieved peak flow and peak time errors of 0.56% and -6.82%, respectively, confirming its feasibility and accuracy.

Abstract:To analyze the influence of building density in urban areas on the transport process of dissolved pollutants, taking conservative dissolved pollutants as the object, a two-dimensional mathematical model for rainfall runoff and pollutant transport in the building area was established, and the effects of different building densities on the mass concentration, transport rate and cumulative transport process of dissolved pollutants were simulated and analyzed. The simulated results show that when the building density ranges from 4% to 16%, the flow rate increases relatively quickly in the middle stage of runoff confluence. With the increase of building density, the water depth downstream of the building gaps first increases and then decreases, and reaches its maximum value at a building density of 36%. The mass concentration of pollutants at the regional outlet generally decreases gradually, while the pollutant transport rate first increases and then decreases. In the case of staggered building arrangements, the upstream pollutants are intermittently transported downstream through the gaps between buildings. When the building density is greater than 9%, the mass concentration and transport rate of pollutants at the regional outlet exhibit multiple fluctuates before the runoff reaches its maximum. With the increase of building density, the transport rate of pollutants decreases and the peak occurrence time is delayed. The final cumulative transport proportion of pollutants decreases with the increase of building density.

Abstract:In order to further explore the failure mechanism of canal slope, triaxial tests and scanning electron microscope (SEM) tests were conducted on expansive soil in northern Xinjiang under dry-wet-freeze-thaw cycle conditions,the physical deterioration mechanism of expansive soil was studied from macroscopic, mesoscopic and microscopic perspectives,and the influence of dry-wet-fueeze-thaw cycles on the parameters of the Duncan-Zhang E-B model was analyzed. The results show that under the dry-wet-freeze-thaw cycle conditions, the stress-strain curve of the expansive soil exhibits a hardening type, and the volumetric strain curve shows shear shrinkage characteristics.The cohesion decreases nonlinearly with the increase of the number of cycles, with the most significant reduction occurring during the first cycle, and it tends to be stable after seven cycles. The internal friction angle changes little and remains almost constant.During the cyclic process, cracks in the expansive soil develop from both ends to the center, the internal crack grids gradually converge and form a crack core in the weak area of the soil body, and the overall failure surface gradually develops from an initial “Y” shape or “X” shape to a “claw-shaped” longitudinal penetration damage surface. The cyclic action caused the aggregated structure of the soil to break down and reorganize into a loose flocculent structure, the intergranular pores increase, and the clay particles gradually peel off and detach, resulting in the structural damage of the soil body. The weakening of the intergranular bonding effect is the main reason for the decrease in cohesion.The cyclic action has significant influence on the Duncan-Zhang E-B model parameters n , K , and K b. When the number of cycles is more than three, the changes in these parameters are relatively small. Exponential function fitting indicates a good correlation between these parameters and the number of cycles.

Abstract:To address the issue of saltwater intrusion in the Qiantang River Estuary significantly affecting water resources utilization, a numerical model for saltwater intrusion capable of simulating tidal bores was constructed. The model was calibrated and validated using two sets of field measurements. The temporal and spatial characteristics of salinity variation in the estuary under changing upstream runoff were analyzed. The results show that during dry seasons, although strong tidal dynamics make it difficult for runoff variations to significantly alter estuarine hydrodynamics, sustained freshwater discharge effectively reduces salinity through cumulative dilution, with the desalination effect decreasing from upstream to downstream. Runoff regulation exerts a rapid and prolonged influence on estuarine salinity, with significant responses emerging within one to two days and persisting far longer than the period of runoff variation. To enhance saltwater suppression efficiency and conserve freshwater resources, it is recommended to increase the suppressing discharge one to two days prior to spring tides and gradually reduce it afterward.

Abstract:To investigate the long-term complementary regulation capability of hybrid pumped-storage power stations under the background of grid integration of large-scale wind and photovoltaic power, an optimal operation model for long-term complementary power generation of wind-photovoltaic-hybrid storage systems was developed. This model aims to maximize the utilization of wind and photovoltaic power generation in the joint operation of wind-photovoltaic-hybrid storage systems by minimizing the variance of residual load, and it was solved using a progressive optimization algorithm. The results of a case study show that compared with the wind-photovoltaic-hydro system without reversible pump-turbine units, the expected value of the utilization rate of wind and photovoltaic power in the wind-photovoltaic-hybrid storage system increases by 8.56%, and the expected value of the variance of residual load decreases by 99.38%. These results indicate that the hybrid pumped-storage power station can better play its role in regulating wind and photovoltaic power, and can improve the utilization rate of wind and photovoltaic power generation and the power generation capacity of the wind-photovoltaic-hybrid storage system while meeting the demand for tracking grid load.

Abstract:In order to achieve a win-win situation for both power generation and ecological benefits of cascade reservoirs, a dynamic simulation chain of “forecasting-scheduling-risk analysis” was constructed. The forecast error evolution process was revealed by the martingale model of forecast evolution (MMFE). The rolling inflow forecast scenarios were generated by the Monte Carlo simulation (MCS) based on Latin hypercube sampling (LHS). Using cascade reservoirs in the Qingjiang River Basin as an example, on the basis of regional hydrological information with uncertainty, the minimum, suitable, and ideal ecological flow rates of the downstream control sections of the Shuibuya and Geheyan reservoirs were calculated, and a synergistic regulation model of power generation and ecological benefit of cascade reservoirs was constructed and solved using the multi-objective shuffling frog leaping algorithm (MOSFLA). The potential risk of water regulation under the influence of runoff forecast uncertainty was analyzed. The results demonstrate that the proposed model can dynamically identify the uncertain information propagated from the inflow forecast to reservoir scheduling, helping to reduce potential water regulation risk and enhance the robustness of water resources regulation for cascade reservoirs.

Abstract:To address the issue of low prediction accuracy caused by uncertainties in the selection of factors and construction of the seepage safety monitoring model for pumped storage power station dams, this study integrated deep learning models with probabilistic prediction methods. By incorporating the feature extraction capability of convolutional neural network (CNN), the data mining potential of bidirectional gated recurrent units (BiGRU), the parameter optimization advantage of the dung beetle optimization (DBO) algorithm, and the probabilistic prediction capability of quartile regression (QR), a probabilistic dam seepage prediction model based on DBO, CNN, BiGRU, and QR was established. At the same time, to construct an optimal factor set suitable for the seepage safety monitoring model for pumped storage power stations, the lag effect of seepage was fully taken into account, and the kernel principal component analysis (KPCA) was adopted to optimize the influencing factors of the model. Engineering case studies demonstrate that the established probabilistic dam seepage prediction model can not only provide high-accuracy deterministic prediction results of dam seepage pressure, but also yield corresponding probabilistic prediction intervals to reflect the uncertainty of seepage changes, which can provide more comprehensive evaluation information for seepage safety monitoring of pumped storage power station dams.

Abstract:Taking the upper Lijiang River Basin, a critical area for flood control and water resources security in Guilin, as the study area, the daily measured rainfall data of 38 rainfall observation stations from 1983 to 2023 were converted into areal rainfall data of 13 spatial sub-basins based on the Thiessen polygon method. The Mann-Kendall trend test and the extreme-point symmetric mode decomposition (ESMD) method were employed to analyze the temporal and spatial evolution characteristics of rainfall across four temporal scales: the entire hydrological year, the main flood season, the post-flood season, and the dry season. The spatial and temporal unevenness of rainfall was revealed based on the temporal and spatial variation coefficients. The results indicate that the annual rainfall and the rainfall during the main flood season increased significantly at rates of 11.36 mm/a and 9.10 mm/a, respectively, while the rainfall in the post-flood season and the dry season showed no significant trend, which enhanced the risk of flooding during the flood season in the upper Lijiang River Basin. The annual distribution of rainfall in the basin was spatially and temporally uneven, and the average temporal variation coefficient of the 13 spatial sub-basins was 2.174, indicating a non-significant increasing trend in temporal inhomogeneity and a widening disparity between wet and dry periods. Spatial variation coefficients exhibited a slightly decreasing trend throughout the entire year, the main flood season, and the dry season, suggesting the spatial distribution of rainfall tends to be more uniform, while spatial inhomogeneity increased slightly during the post-flood season, complicating the regulation of reservoir groups during this period. The rainfall in the upper Lijiang River Basin has exhibited distinct and inconsistent changes at different temporal and spatial scales. These changes increase the complexity of flood control and beneficial operation for the upstream reservoir groups, elevate the challenge for urban flood control in Guilin, and introduce greater uncertainty in the ecological landscape flow guarantee of the Lijiang River.

Abstract:To investigate the effects of green roof retrofitting, the Tianfu Heyuan residential community in Fengxi New City was selected as the study area. A numerical model coupling hydrological and hydrodynamic processes was applied. Six rainfall return periods (1, 2, 5, 10, 20, and 30 years) were selected, along with five different green roof retrofit area scenarios, resulting in 30 retrofit conditions to examine the impact on runoff. The results show that green roof retrofitting can effectively mitigate surface waterlogging. When the rainfall return period remains constant and the retrofit area is maximized, the runoff control rate of green roofs can be increased by 11.09% to 16.20%, the peak flow reduction rate can reach 17.66% to 68.45%, the outlet peak flow reduction rate can increase to 17.49% to 37.40%, and the contribution rate of the green roof retrofitting can reach 14.20% to 16.77%. Meanwhile, the contribution rate at the outlet decreases as the retrofit area increases. When the retrofit area remains unchanged and the rainfall return period increases, both the green roof peak flow reduction rate and its contribution rate show a trend of first increasing and then decreasing, with the best effect observed at a 5-year return period, where the peak flow reduction rate can reach 68.45% and the contribution rate can reach 16.77%. The outlet peak flow reduction rate shows a trend of first decreasing, then increasing, and then decreasing again, with inflection points at the 5-year and 20-year return periods. The contribution rate at the outlet shows an overall increasing trend.

Abstract:To investigate the effects of different irrigation regimes for winter wheat during the rotation period on the water use efficiency (WUE) of rainfed summer maize in the Heilonggang River Basin of the North China Plain, five irrigation regimes were established during the winter wheat growing season: with no irrigation (IS0), irrigation at the jointing stage (IS1), irrigation at jointing and flowering stages (IS2), irrigation at erecting, flowering, and grain filling stages (IS3), and irrigation at erecting, jointing, flowering, and grain filling stages (IS4). The study analyzed the impacts of these irrigation regimes on soil water dynamics, effective rainfall utilization, water consumption characteristics, yield, and WUE of subsequent summer maize. A comprehensive evaluation was conducted using the TOPSIS-entropy weight method based on four indicators: water consumption, rainfall utilization efficiency, yield, and WUE. The results show that soil water content during the summer maize season was lowest in the 0-30.cm layer, highest in the 30-60.cm layer, and relatively low in the 60-100.cm layer. Rainfall utilization efficiency during the summer maize growing season decreased with increasing winter wheat irrigation frequency. IS0 had the highest rainfall utilization efficiency of 54.31%, while IS1, IS2, IS3, and IS4 showed decreases of 7.81%, 24.98%, 27.49%, and 28.32%, respectively, compared to IS0. Total water consumption during the summer maize season increased with winter wheat irrigation frequency, with IS1, IS2, IS3, and IS4 increasing by 5.98%, 7.23%, 14.35%, and 20.77%, respectively, compared to IS0. Except for IS2, summer maize grain yield generally increased with winter wheat irrigation frequency, whereas WUE decreased. IS2 achieved the highest grain yield (17 593.87.kg/hm²) and WUE (3.43.kg/m³). IS2 had the highest relative closeness (approximately 0.60), making it the optimal irrigation regime. In conclusion, irrigating winter wheat twice during the jointing and flowering stages (IS2, with total irrigation of 150 mm) can ensure high summer maize yield while conserving water and effectively utilizing rainfall resources, thereby improving overall WUE during the crop rotation.